Method of protecting light-metal surfaces



Patented July 7, 1942 METHOD OF PROTECTING LIGHT-METAL SURFACES Percy Frederick George, Midland, Mich, assignor to the Dow Chemical Company,

Midland,

Mich, a corporation of Michigan No Drawing. Application December 23, 1940, Serial No. 371,391

6 Claims.-

This invention relates to a method and means for protecting surfaces of light-metals, especially magnesium and magnesium-base alloys and aluminum and aluminum-base alloys, against corrosive attack by water and water-containing media.

As is known, surfaces of magnesium and magnesium-base alloys, and to a lesser extent also of aluminum and aluminum-base alloys, are corroded by contact with aqueous media, such as acidic or saline solutions. This corrosion is particularly evident in containers, the inner surfaces of which are formed of magnesiumor aluminumbase alloys, which are used in storing liquid hydrocarbons, such as motor fuels and lubricants. In such use there is normally present on the bottom of the container an aqueous phase, consisting principally of moisture condensed from the atmosphere and precipitated from the hydrocarbon by temperature change. This aqueous condensate tends to dissolve any corrosive substances occurring in the hydrocarbon, and, over extended periods of time, attacks the inner surfaces of the container to a marked degree. Corrosion is especially serious when the motor fuel contains anti-knock fluid, e. g. tetra-ethyl lead and ethylene dibromide.

In view of these facts, it is an object of the present invention to provide a simple method and means for substantially preventing corrosion of the character described.

The invention is based upon the discovery that the corrosion of magnesium and magnesium-base alloys and of aluminum and aluminum-base alloys by an aqueous fluid in contact therewith can be substantially prevented by adding tothe fluid an alkaline water-soluble metal salt of a glycoside.

The glycoside salts referred to are the salts formed by reacting glycosides derived from natural sources with metal compounds, such as metal hydroxides. Such salts are ordinarily obtained in somewhat impure form, usually as sirupy liquids. Only those salts which are soluble in water, i. e. which mix readily with water to form an actual solution or a uniform colloidal suspension, and which, in water solutions exhibit an alkaline reaction, are useful in the present invention. Maximum inhibiting value is obtained with salts of the beta-glucosides derived from vegetable sources, such as succulent plants; these beta-glucosides, as is known, correspond to the general formula CHORCHOH. CHOH.CH.CHOH.CH2OH wherein R. is a long chain organic radical. (Ind. Eng. Chem. 30, 1356-61 (1938), and Or anic Methods of Scale and Corrosion Control, D. W. Haering & 00., 3rd edition, Chicago, 1939, page 9.) The alkali metal or chromium-containing salts of such beta-glucosides, which are commercially available under the names sodium glucosate, sodium chrom glucosate, etc., and correspond to the formulae CH0R.CHONa.CHOH.CH.CHONa.CH2OH sodium glucosate O (JHORCHONaCHOllCELCHOCrzOaNaCHzOEL sodium chrom glucosate I wherein R is a long chain organic radical, are particularly effective.

In general, the glycoside salts are employed in a proportion of 0.2 to 5.0 per cent by weight of the liquid to which they are added, although other quantities are sometimes efiective in substantially retarding corrosion, as can be determined by simple test.

In practice, in preventing the corrosive attack on magnesiumand aluminum-alloy tanks containing hydrocarbon fuel in contact with the aqueous condensate normally present in such tanks, the glycoside salt is merely inserted into the tank in such position as to be in contact with any aqueous phase. The glycoside salt dissolves in the water and thus substantially inhibits corrosion of the metal. The glycoside salt, being sirupy, may be conveniently introduced through a suitable fitting by means of an ordinary grease gun.

While the principle of the invention has been described primarily with respect to preventing the corrosion of containers in which hydrocarbon liquids are stored in contact with water, and is particularly useful in this regard, it will be understood that the invention is broadly applicable to preventing the corrosion of magnesium and magnesium-base alloys by water and water-containing media. For instance, the corrosion of fuel tanks in contact with water-containing alcohol-blended motor fuel may be retarded by dissolving a glycoside salt of the character described in the fuel. Likewise, the glycoside salt may be introduced into the cooling systems of internal combustion engines having magnesiumor aluminum-alloy parts in such systems when employing water or an aqueous alcohol or glycol as the cooling medium, thereby preventing corrosive attack. Other specific applications of the invention will doubtless occur to those skilled in the art.

The following example will serve to illustrate the invention:

Example 7 of sodium glucosate was introduced into the tank, there was no observable corrosion after 75 days.

Similar results were obtained in tests carried out on tanks formed of Dowmetal M (an alloy of 98.5 per cent magnesium and 1.5 per cent manganese).

I claim:

1. A method of retarding the-corrosive attack 2 upon a metal selected from the. class consisting of magnesium and magnesium-base alloys and aluminum and aluminum-base alloys by an aqueousfiuid in contact therewith which comprises adding to said fluid an alkaline watersoluble metal salt of a 'b'e'ta-g'luc'os'ide derived from a succulent plant in a proportion sufficient substantially to retard corrosion.

2. A method of protecting a container, the inner surfaces of which are formed of a metal se- 35 lected from the class consisting of magnesium and magnesium-base alloys and aluminum and aluminum-base alloys, against corrosive attack by a system stored therein consisting essentially of a liquid hydrocarbon in contact with an aqueous phase which comprises introducing into the container in contact with the aqueous phase an alkaline water-soluble metal salt of a beta-glucoside derived from a succulent plant.

3. A method of protecting a fuel tank formed of a magnesium-base alloy against corrosive attack by a liquid system stored therein consisting of hydrocarbon fuel containing tetra-ethyl lead anti-knock fluid in contact with the aqueous condensate normally present in the tank which comprises inserting into the tank in contact with the aqueous phase an alkaline water-soluble metal salt of a beta-glucoside. derived from a succulent plant.

4. A method according to claim 3 wherein the alkaline glucoside salt is sodium glucosate.

5. A method according to claim 3 wherein the alkaline glucoside salt is sodium chrom glucosate.

6. A method of protecting a container, the inner surfaces of which are formed of a metal selected from the class consisting of magnesium and magnesium-base alloys. and aluminum and aluminum-base alloys, against corrosive attack by a water-containing alcohol-blended hydrocarbon motor fuel stored therein which comprises introducing into the container in contact with the fuel an alkaline water-soluble metal salt of a beta-glucoside derived from asucculent plant.

PERCY FREDERICK GEORGE. 

